Helicobacter suis Infection in Mouse Induced not Only Gastric, but Hepatic and Pulmonary MALT Lymphoma: Relation to Substance P

Background: The hepatic and pulmonary MALT lymphoma (mucosa-associated lymphoid tissue lymphoma) is clinically occasionally observed but its pathogenesis is unknown and thought to be important to establish the treatment strategy. Objectives: The present study was designed to clarify the characteristics of these lymphomas and the effect of the Helicobacter eradication regimen and substance P antagonist. Methods: After the long term infection of Helicobacter suis to the C57BL/6 mice stomach, the whole organ was surveyed pathologically. Histochemical characteristics of the lesion and the localization of bacteria were observed. In addition, the effect of the administration of antibiotics and a proton pump inhibitor or the substance P antagonist was investigated. Results: We have detected the hepatic and pulmonary MALT lymphoma after the long term infection. In situ hybridization study revealed the positive reaction of Helicobacter suis in the hepatic and pulmonary MALT lymphoma. After the administration of antibiotics and a proton pump inhibitor, the bacterial number has significantly decreased and the tumor size in the fundus, liver and lung markedly reduced. Substance P immunoreactivity was clearly shown in the lymphoma cells in the liver and lung, and the spantide II administration induced the marked decrease in the size of tumors. Conclusion: By our experiments using the long term infection of Helicobacter suis to the C57BL/6 mice, we have detected the liver and pulmonary MALT lymphoma. In situ hybridization study suggested the direct interaction of this bacterium to the etiology of these lesions. Substance P within the lymphoma cells was suggested to work on the maintenance of the extragastric MALT lymphoma.